<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>

    <style>
      .box1 {
        width: 200px;
        height: 200px;
        background-color: #bfa;
      }
      .box2 {
        width: 100px;
        height: 100px;
        background-color: blue;
        margin-top: 100px;
      }

      .clearfix::before,
      .clearfix::after {
        content: "";
        display: table;
        clear: both;
      }
      /* clearfix这个样式可以同时解决高度塌陷和外边距重叠的问题，当你在遇到这些问题时，直接使用clearfix */
    </style>
  </head>
  <body>
    <div class="box1 clearfix">
      <div class="box2"></div>
    </div>
  </body>
</html>
